U.S. patent number 9,306,099 [Application Number 12/956,964] was granted by the patent office on 2016-04-05 for material including graphene and an inorganic material and method of manufacturing the material.
This patent grant is currently assigned to KUMOH NATIONAL INSTITUTE OF TECHNOLOGY INDUSTRY-ACADEMIC COOPERATION FOUNDATION, SAMSUNG ELECTRONICS CO., LTD.. The grantee listed for this patent is Duk-hyun Choi, Jae-young Choi, Won-mook Choi, Sang-woo Kim, Kyung-sik Shin. Invention is credited to Duk-hyun Choi, Jae-young Choi, Won-mook Choi, Sang-woo Kim, Kyung-sik Shin.
United States Patent |
9,306,099 |
Choi , et al. |
April 5, 2016 |
Material including graphene and an inorganic material and method of
manufacturing the material
Abstract
A material including: graphene; and an inorganic material having
a crystal system, wherein a crystal plane of the inorganic material
is oriented parallel to the (0001) plane of the graphene. The
crystal plane of the inorganic material has an atomic arrangement
of a hexagon, a tetragon, or a pentagon.
Inventors: |
Choi; Jae-young (Suwon-si,
KR), Choi; Won-mook (Hwaseong-si, KR),
Choi; Duk-hyun (Hwaseong-si, KR), Kim; Sang-woo
(Gumi-si, KR), Shin; Kyung-sik (Daejeon,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Choi; Jae-young
Choi; Won-mook
Choi; Duk-hyun
Kim; Sang-woo
Shin; Kyung-sik |
Suwon-si
Hwaseong-si
Hwaseong-si
Gumi-si
Daejeon |
N/A
N/A
N/A
N/A
N/A |
KR
KR
KR
KR
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO., LTD.
(KR)
KUMOH NATIONAL INSTITUTE OF TECHNOLOGY INDUSTRY-ACADEMIC
COOPERATION FOUNDATION (KR)
|
Family
ID: |
44069114 |
Appl.
No.: |
12/956,964 |
Filed: |
November 30, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110129675 A1 |
Jun 2, 2011 |
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Foreign Application Priority Data
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Dec 1, 2009 [KR] |
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10-2009-0117834 |
Nov 30, 2010 [KR] |
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10-2010-0120515 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
31/035227 (20130101); H01L 31/036 (20130101); C01B
32/182 (20170801); C01B 2204/00 (20130101); Y10T
428/30 (20150115) |
Current International
Class: |
B32B
9/00 (20060101); H01L 31/0352 (20060101); H01L
31/0392 (20060101); H01L 31/036 (20060101); C01B
31/04 (20060101) |
Field of
Search: |
;257/29 ;438/478
;428/408 ;423/448 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1020080100430 |
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Feb 2008 |
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KR |
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1020090017454 |
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Feb 2009 |
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KR |
|
1020090043418 |
|
May 2009 |
|
KR |
|
2009/120151 |
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Oct 2009 |
|
WO |
|
Primary Examiner: Miller; Daniel H
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
What is claimed is:
1. A material comprising: a substrate; graphene disposed on the
substrate; and an inorganic material having a crystal system and
disposed on the graphene, wherein at least one crystal plane of the
inorganic material is oriented parallel to a (0001) plane of the
graphene, wherein the inorganic material is disposed directly on
the graphene, and wherein a difference between a distance between
atoms at first and third sites in a hexagon atomic arrangement of
the inorganic material and a distance between carbon atoms at first
and fourth sites of a hexagonal repeating unit of the graphene is
about -10 percent to about 20 percent of the distance between the
carbon atoms at the first and fourth sites of the hexagonal
repeating unit of the graphene, wherein the inorganic material
comprises ZnO.
2. The material of claim 1, wherein the crystal plane of the
inorganic material has an atomic arrangement of a hexagon.
3. The material of claim 1, wherein the crystal system of the
inorganic material is a hexagonal system.
4. The material of claim 2, wherein the difference between the
distance between the atoms at the first and third sites in the
hexagon atomic arrangement of the inorganic material and the
distance between the carbon atoms at first and fourth sites of the
hexagonal repeating unit of the graphene is about 10 percent to
about 20 percent of the distance between the carbon atoms at the
first and fourth sites of the hexagonal repeating unit of the
graphene.
5. The material of claim 2, wherein a first axis between the first
and third atoms of the hexagon atomic arrangement of the inorganic
material and a second axis between the first and fourth atoms of
the graphene are oriented in a substantially same direction.
6. The material of claim 1, wherein the inorganic material is an
epitaxial layer on the graphene.
7. The material of claim 1, wherein the graphene has a sheet shape
and an area of equal to or greater than 1 square millimeter.
8. An electrical device comprising the material of claim 1.
9. A material comprising: a substrate having a surface; an
inorganic material having a crystal system, wherein at least one
crystal plane of the inorganic material is oriented to be parallel
to the surface of the substrate; and graphene interposed between
the surface of the substrate and the inorganic material, wherein at
least one crystal plane of the inorganic material is oriented
parallel to the (0001) plane of the graphene, wherein a difference
between a distance between atoms at first and third sites in a
hexagon atomic arrangement of the inorganic material and a distance
between carbon atoms at first and fourth sites of a hexagonal
repeating unit of the graphene is about -10 percent to about 20
percent of the distance between the carbon atoms at the first and
fourth sites of the hexagonal repeating unit of the graphene,
wherein the inorganic material comprises ZnO.
10. The material of claim 9, wherein the crystal plane of the
inorganic material has an atomic arrangement of a hexagon.
11. The material of claim 9, wherein the crystal system of the
inorganic material is a hexagonal system.
12. The material of claim 10, wherein the difference between the
distance between the atoms at the first and third sites in the
hexagon atomic arrangement of the inorganic material and the
distance between the carbon atoms at the first and fourth sites of
a hexagonal repeating unit of the graphene is about 10 percent to
about 20 percent of the distance between carbon atoms at first and
fourth sites of the hexagonal repeating unit of the graphene.
13. The material of claim 10, wherein a first axis between the
first and third atoms of the hexagon atomic arrangement of the
inorganic material and a second axis between the first and fourth
atoms of the graphene are oriented in a substantially same
direction.
14. The material of claim 9, wherein the inorganic material is an
epitaxial layer on the graphene.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application
No. 10-2009-0117834, filed on Dec. 1, 2009, and 10-2010-0120515,
filed on Nov. 30, 2010, and all the benefits accruing therefrom
under 35 U.S.C. .sctn.119, the content of which in its entirety is
herein incorporated by reference.
BACKGROUND
1. Field
This disclosure relates to a material including graphene and an
inorganic material and a method of manufacturing the material, and
in particular, to a material having improved electrical
characteristics.
2. Description of the Related Art
Generally, graphite has a structure in which two-dimensional ("2D")
graphene sheets are stacked parallel to each other to form a
three-dimensional crystalline material. The graphene sheets have a
planar shape in which carbon atoms are connected to each other in a
hexagonal configuration. Recently, the characteristics of a single
sheet of graphene or a few sheets of graphene, which were peeled
off of graphite, were evaluated in several studies. The evaluations
found that the characteristics of graphene are very different from
the characteristics of conventional materials.
For example, the electrical characteristics of graphene are
anisotropic, and thus depend on the crystallographic orientation of
the graphene. The anisotropy enables selection of the electric
characteristics by using graphene in a selected direction, and thus
the selected electrical characteristics may be utilized in a
carbonaceous electrical device or in a carbonaceous electromagnetic
device.
However, when a device is manufactured by depositing a material on
graphene, the structure of the interface between graphene and the
deposited material greatly affects the characteristics of the
manufactured device. In addition, when an electrical charge flows
between graphene and the deposited material, a defect at the
interface between the graphene and the deposited material may
result in interfacial resistance between graphene and the deposited
material. Thus, in order to effectively use the excellent
electrical conductivity of graphene, materials in which interfacial
defects are minimized are needed.
SUMMARY
Provided is a material of graphene and an inorganic material which
is manufactured at low cost and of which an interface has reduced
defects and electrical resistance.
Provided is a method of manufacturing the material.
Provided is an electrical device including the material.
Additional aspects, features, and advantages will be set forth in
part in the description which follows and, in part, will be
apparent from the description.
According to an aspect, a material includes graphene; and an
inorganic material having a crystal system, wherein at least one
crystal plane of the inorganic material is oriented parallel to the
(0001) plane of the graphene.
The material may further include a substrate on the graphene.
The crystal plane of the inorganic material may have an atomic
arrangement of a hexagon, a tetragon, or a pentagon.
The crystal system of the inorganic material is a cubic system, a
tetragonal system, a hexagonal system, an orthorhomic system, a
rhomoboheral system, a monoclinic system, or a triclinic
system.
The inorganic material may include at least one of Ge, Si, Sn, SiC,
AlAs, AlP, AlSb, Al.sub.2O.sub.3, BN, BP, GaAs, GaN, GaP, GaSb,
GaNO, InN, InNO, InAs, InP, InSb, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe,
ZnTe, PbS, PbTe, AlN, BNO, MgS, MgSe, or MgTe.
The inorganic material may include at least one of ZnO, GaN,
Al.sub.2O.sub.3, or a combination thereof.
A distance between atoms at first and third sites in the hexagon
atomic arrangement of the inorganic material may be about -20
percent to about 20 percent of a distance between carbon atoms at
first and fourth sites of a hexagonal repeating unit of the
graphene.
A shorter axis of the hexagon atomic arrangement of the inorganic
material and a longer axis of the graphene may be oriented in a
substantially same direction.
The inorganic material may be an epitaxial layer on the
graphene.
The graphene may have a sheet shape and an area of equal to or
greater than about 1 square millimeter.
Also disclosed is an electrical device including the foregoing
material.
According to an aspect, a material includes: a substrate having a
surface; an inorganic material having a crystal system, wherein at
least one crystal plane of the inorganic material is oriented to be
parallel to the surface of the substrate; and graphene interposed
between the surface of the substrate and the inorganic
material.
BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other aspects will become apparent and more readily
appreciated from the following description of the embodiments,
taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic view illustrating a hexagonal unit cell;
FIG. 2A is a schematic view illustrating an embodiment of an
interface of graphene and an inorganic material;
FIG. 2B is an enlarged view of the indicated region of FIG. 2A;
FIG. 2C is a schematic view illustrating an embodiment of an
interface of graphene and an inorganic material;
FIG. 2D is an enlarged view of the indicated region of FIG. 2C;
FIGS. 3A and 3B are schematic views illustrating distances in a
hexagonal repeating unit of graphene and in a hexagonal repeating
unit of an inorganic material, respectively;
FIG. 4 is a schematic view illustrating the structure of an
embodiment of a material comprising graphene and an inorganic
material;
FIG. 5 is a scanning electron microscope ("SEM") image of a ZnO
nanorod vertically grown with respect to a surface of graphene,
according to Example 1;
FIG. 6A is a transmission electron microscope ("TEM") image of an
interface between a ZnO nanorod and graphene, according to Example
1;
FIG. 6B is an enlarged view of the indicated portion of FIG.
6A;
FIG. 6C is a selected area diffraction pattern of the upper
indicated (i.e., ZnO) portion of FIG. 6B;
FIG. 6D is a selected area diffraction pattern of the lower
indicated (i.e., graphene) portion of FIG. 6B;
FIG. 7A is a graph of current density (microamperes per square
centimeter, .mu.A/cm.sup.2) versus time (seconds) illustrating
characteristics of a nanoscale power generator including an indium
tin oxide ("ITO")-coated substrate manufactured according to
Example 2; and
FIG. 7B is a graph of current density (microamperes per square
centimeter, .mu.A/cm.sup.2) versus time (seconds) illustrating
characteristics of a nanoscale power generator including
graphene-coated substrate manufactured according to Example 2.
DETAILED DESCRIPTION
Reference will now be made in detail to embodiments, examples of
which are illustrated in the accompanying drawings, wherein like
reference numerals refer to the like elements throughout. In this
regard, the present embodiments may have different forms and should
not be construed as being limited to the descriptions set forth
herein. Accordingly, the embodiments are merely described below, by
referring to the figures, to explain aspects of the present
description.
It will be understood that when an element is referred to as being
"on" another element, it can be directly on the other element or
intervening elements may be present therebetween. In contrast, when
an element is referred to as being "directly on" another element,
there are no intervening elements present. As used herein, the term
"and/or" includes any and all combinations of one or more of the
associated listed items.
It will be understood that, although the terms first, second, third
etc. may be used herein to describe various elements, components,
regions, layers and/or sections, these elements, components,
regions, layers and/or sections should not be limited by these
terms. These terms are only used to distinguish one element,
component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section discussed below could be termed
a second element, component, region, layer or section without
departing from the teachings of the present invention.
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, the singular forms "a," "an" and "the" are intended to
include the plural forms as well, unless the context clearly
indicates otherwise. It will be further understood that the terms
"comprises" and/or "comprising," or "includes" and/or "including"
when used in this specification, specify the presence of stated
features, regions, integers, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, regions, integers, steps, operations,
elements, components, and/or groups thereof.
Spatially relative terms, such as "beneath," "below," "lower,"
"above," "upper" and the like, may be used herein for ease of
description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, the
exemplary term "below" can encompass both an orientation of above
and below. The device may be otherwise oriented (rotated 90 degrees
or at other orientations) and the spatially relative descriptors
used herein interpreted accordingly.
Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
Exemplary embodiments are described herein with reference to cross
section illustrations that are schematic illustrations of idealized
embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, embodiments described
herein should not be construed as limited to the particular shapes
of regions as illustrated herein but are to include deviations in
shapes that result, for example, from manufacturing. For example, a
region illustrated or described as flat may, typically, have rough
and/or nonlinear features. Moreover, sharp angles that are
illustrated may be rounded. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the precise shape of a region and are not intended to
limit the scope of the present claims.
Herein, crystal planes of materials are identified by their Miller
indices unless otherwise indicated.
In a material comprising graphene and an inorganic material, a
crystal plane of an inorganic material having a crystal structure
is oriented to be substantially parallel to the (0001) plane of
graphene.
The term "graphene" as used in the present specification means a
polycyclic aromatic molecule formed from a plurality of carbon
atoms which are covalently bound to each other. The covalently
bound carbon atoms may form a six-membered ring as a repeating
unit, and may further include at least one of a five-membered ring
and a seven-membered ring. Accordingly, graphene comprises a single
layer of covalently bonded carbon atoms having sp.sup.2
hybridization. A plurality of graphene layers is often referred to
in the art as graphite. However, for convenience, "graphene" as
used herein may be a single layer, or also may comprise a plurality
of layers of carbon. Thus graphene, as used herein, may have a
multiply layered structure formed by stacking single layers of
graphene. The maximum thickness of the graphene may be about 100
nanometers (nm), specifically 90 nm, more specifically 80 nm.
The repeating unit of graphene is a six-membered ring containing
six carbon atoms, and a plurality of the six-membered rings are
connected to each other to provide a planar structure. When
multiple layers are present, the layers are stacked on each other.
Because the six-membered ring structure is similar to a hexagonal
prism structure, a plane index and a direction index of the
hexagonal prism structure may also be applied to the six-membered
graphene ring structure. As illustrated in FIG. 1, a unit cell of
the hexagonal prism lattice has a.sub.1, a.sub.2, and a.sub.3 axes,
which are at an angle of 120.degree. relative to each other and on
a same plane, and a c axis that is perpendicular to the plane of
the a.sub.1, a.sub.2, and a.sub.3 axes. Thus, each plane index
(i.e., Miller-Bravais index) and direction index of the hexagonal
prism structure has four indices that correspond to the four axes.
For example, a reference plane of a six-membered ring of graphene
that has a 2-dimensional structure may be the plane of the axes
a.sub.1, a.sub.2, and a.sub.3 that is shadowed in FIG. 1 and the
plane may have an index of (0001). A surface of a material may
correspond to a plane having a particular plane index. Thus, for
example, a (001) plane of a material is understood to refer to a
surface corresponding to a (001) plane.
The inorganic material, which may be for example, a metal or a
metal oxide, may have a various crystal system such as a cubic
system, a tetragonal system, a hexagonal system, an orthorhomic
system, a rhomoboheral system, a monoclinic system, or a triclinic
system. The crystal system may comprise crystal planes
characterized by their Miller indices.
The crystal planes of the inorganic material may have a various
atomic arrangement such as a hexagon, a tetragon, or a pentagon as
a unit cell.
In an embodiment, the at least one crystal plane of the inorganic
material having the various crystal system can be oriented parallel
to the (0001) plane of graphene, and thus the selected layer of the
inorganic material may be oriented substantially parallel to the
(0001) plane of graphene.
Examples of the material described above are illustrated in FIGS.
2A to 2D. FIGS. 2A and 2B illustrate an exemplary embodiment of an
inorganic material 10 layer disposed (e.g., formed) on graphene 20.
In an embodiment, the inorganic layer may be an epitaxial layer on
the graphene. Referring to FIGS. 2A and 2B, an inorganic material
may be formed such that at least one crystal plane of the inorganic
material is parallel to and in direct contact with the (0001) plane
of the graphene. FIGS. 2C and 2D illustrate an example of an
inorganic material rod 11 disposed (e.g., formed) on graphene 21.
In an embodiment, the graphene may be epitaxial, thus the crystal
structure of the inorganic material rod and the graphene may have a
substantially same orientation. Referring to FIGS. 2C and 2D, an
inorganic material may be disposed (e.g., grown) such that a
crystal plane of the inorganic material is oriented parallel to and
directly on the (0001) plane of the graphene, for example.
In order to orient the inorganic material so that a selected plane
is parallel to the (0001) plane of the graphene, the crystal
structure of the inorganic material desirably also may have an
atomic arrangement of a hexagon, a tetragon, or a pentagon as a
unit cell.
An exemplary inorganic material includes Ge, Si, Sn, SiC, AlAs,
AlP, AlSb, Al.sub.2O.sub.3, BN, BP, GaAs, GaN, GaP, GaSb, GaNO,
InN, InNO, InAs, InP, InSb, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe,
PbS, PbTe, AlN, BNO, MgS, MgSe, MgTe, or a combination thereof.
As is further disclosed above, the selected plane of the inorganic
material is oriented to be parallel to the selected surface of the
graphene, and in this orientation, the inorganic material may be
formed as, for example, an epitaxial structure. In an embodiment,
the c axis of the graphene may be substantially perpendicular to
the selected surface of the inorganic material.
When the inorganic material has a hexagon atomic arrangement as a
unit cell in one crystal plane, a longer axis 30 of graphene and a
shorter axis 40 of the inorganic material are defined as
illustrated in FIGS. 3A and 3B, respectively, for an embodiment
wherein the inorganic material is ZnO, for example, although the
inorganic material is not limited thereto. FIG. 3A illustrates a
repeating unit of graphene having a six-membered ring structure,
wherein an axis between a carbon atom at a first site C1 and a
carbon atom at a fourth site C4 is defined as a longer axis of
graphene, which may be about 2.852 .ANG.. A distance between atoms
at the first and third sites of a six-membered ring structure of
the inorganic material is defined as a shorter axis. For example,
FIG. 3B illustrates the crystal structure of a repeating unit of
ZnO, wherein a length between oxygen atoms at first and third sites
is the shorter axis, and may be about 3.261 .ANG.. In the disclosed
epitaxial structure, the longer axis of graphene and the shorter
axis of the inorganic material are substantially aligned. Also, in
an embodiment in which the inorganic material is ZnO, the
difference in length between the longer axis of graphene and the
shorter axis of the inorganic material (ZnO) is about 0.409 .ANG.,
which is about 14.3 percent (%) of the length of the longer axis of
graphene. Thus the length of the longer axis of graphene and length
of the shorter axis of the inorganic material are similar to each
other. However, a distance between adjacent carbon atoms in
graphene is about 1.425 .ANG. and a distance between adjacent Zn
and O atoms in ZnO is about 1.995 .ANG., and thus the difference in
distance is about 0.570 .ANG., which is about 40.0% of the length
of longer axis of graphene.
Thus, when the inorganic material is disposed (e.g., formed) on the
graphene, the inorganic material and the graphene are oriented such
that the shorter axis of the inorganic material is substantially
aligned with the longer axis of the graphene, and thus the
inorganic material may be disposed to have a planar structure which
is substantially parallel to the graphene, which has a
substantially 2-dimensional structure.
The difference between a length of the longer axis of graphene and
a length of the shorter axis of the inorganic material having a
hexagon atomic arrangement as a unit cell may be about -20% to
about 20% of the length of the longer axis of graphene,
specifically about -15% to about 15%, more specifically about -10%
to about 10%. Within this range, the inorganic material and the
graphene are oriented such that the shorter axis of the inorganic
material is substantially aligned with the longer axis of the
graphene.
An exemplary embodiment of the structure disclosed above is
illustrated in FIG. 4. Referring to FIG. 4, dashed circles 50
represent points where the C1 and C4 atoms of the graphene and the
atoms at the first and third sites in the inorganic material
correspond. Thus atoms at the first and third sites in the
inorganic material may correspond to the oxygen atoms in ZnO, for
example. Therefore the longer axis of the graphene may
substantially correspond to the shorter axis of the inorganic
material, as indicated by a corresponding axis 60. Accordingly,
when the graphene and the inorganic material are disposed to have
the foregoing configuration, the inorganic material may have a
selected plane oriented parallel to a selected surface of the
graphene. Also, as illustrated in FIG. 4, all of the longer axes of
graphene may not correspond to all of the shorter axes of the
inorganic material. In addition, all of the shorter axes of the
inorganic material may not correspond all of the longer axes of the
graphene. Thus only a portion of the longer axes of the graphene
may correspond to a portion of the shorter axes of the inorganic
material.
While not wanting to be bound by theory, it is understood that due
to the parallel structure of the graphene and the inorganic
material in the disclosed material, the graphene and the inorganic
material have a substantially constant orientation and thus a
quantity of defects that may occur at the interface between the
graphene and the inorganic material may be minimized. As a result
of the above parallel structure, when a material of the inorganic
material and the graphene is formed, a possibility that these are
grown in a vertical direction or a diagonal direction can be
reduced, and structural defects at the interface of the graphene
and the inorganic material may be substantially eliminated or
effectively reduced.
In the structure, the inorganic material may be disposed in a
one-atom-thick planar sheet or may be disposed to have a thickness
of about 10 centimeters (cm). Thus the inorganic material may have
a thickness of about 1 nm to about 10 cm, specifically 100 nm to
about 1 cm, more specifically 1 micrometer to about 0.1 cm. The
inorganic material may be disposed in the form of a rod, a wire, a
thin film, or a bulk structure. For example, the inorganic material
may be disposed in the form of a nanorod, a nanowire, a nanofilm, a
thin film, or a bulk material, or a combination comprising at least
one of the foregoing.
Because defects at the interface of the graphene and the inorganic
material are reduced, as further disclosed above, an electric
charge (e.g., an electric charge carrier such as an electron or a
hole), may more efficiently flow across the interface, and
accordingly, an interfacial resistance may be reduced. The reduced
interfacial resistance may lead to improved efficiency of an
electrical device including the material, which comprises graphene
and the inorganic material. Exemplary electrical devices include,
for example, a light emitting diode ("LED"), a solar cell, a power
generating device, or a nanoscale power generator, such as a
piezoelectric sensor or a piezoelectric generator, for example.
The material may be disposed (e.g., formed) on various substrates.
For example, the material may be disposed on a substrate comprising
a metal, a metalloid, or an insulator, or a combination comprising
at least one of the foregoing. The substrate may comprise an
inorganic material such as silicon (Si), a glass, GaN, a silica,
indium tin oxide ("ITO"), or a combination thereof (e.g. a silicon
layer/silica layered substrate). The substrate may comprise an
organic material such as a plastic. The metal may include nickel,
copper, tungsten, or a combination comprising at least one of the
foregoing.
A method of manufacturing the material comprising graphene and the
inorganic material will be further disclosed in detail.
First, graphene may be prepared according to a method which may be
determined by one of skill in the art without undue
experimentation. In an embodiment, for example, the graphene may be
prepared by a method disclosed in Korean Patent Publication No.
2009-0043418, the content of which in its entirety is herein
incorporated by reference. For example, a Ni foil having the
dimensions of about 1.2 centimeters (cm) by about 1.5 cm by about
0.5 millimeter (mm) may be disposed (e.g., deposited) in a chamber,
and the Ni foil heat-treated at about 1000.degree. C. for about 5
minutes using a halogen lamp while acetylene gas is added to the
chamber at a constant rate of about 200 standard cubic centimeters
per minute (sccm) to form graphene. Then, a 10 layered graphene
sheet having the dimensions of about 1.2 cm by about 1.5 cm may be
provided by removing the heat source and naturally cooling the
interior of the chamber to grow graphene in a uniform arrangement.
Then, the substrate including the graphene sheet may be immersed in
about 0.1 M HCl for about 24 hours to remove the Ni foil. The
graphene sheet may separate from the Ni foil during the
immersion.
The graphene may have a surface having an area of equal to or
greater than about 1 square millimeter (mm.sup.2), for example, an
area of about 1 mm.sup.2 to about 100 m.sup.2, specifically about 1
mm.sup.2 to about 25 m.sup.2, more specifically about 5 mm.sup.2 to
about 1 m.sup.2. In addition, the graphene may occupy equal to or
greater than about 99% of a selected unit area, specifically about
99% to about 99.999% of a selected unit area, more specifically
about 99.9% to about 99.99% of a selected unit area. When graphene
occupies about 99% of a selected unit area, the graphene may be
uniform, and thus, uniform electrical characteristics may be
obtained. The graphene may have a purity of about 99% to about
99.9999%, specifically about 99.9% to about 99.999%, more
specifically about 99.99%.
A layer of the inorganic material is disposed (e.g., formed) on the
graphene by contacting the graphene with a solution comprising the
inorganic material. The contacting may be performed by immersing,
dipping, coating, or spraying. In an embodiment the layer of the
inorganic material is formed from the solution in such a way that a
(0001) plane of the inorganic material is oriented parallel to a
(0001) plane of the graphene.
The solution comprising the inorganic material may comprise a
solvent. The solvent may be any solvent that disperses or dissolves
the inorganic material. Examples of the solvent may include
ethanol, methanol, acetone, water, or a combination comprising at
least one of the foregoing, and a concentration of the solvent may
be about 0.001 molar (M) to about 1.0 M, specifically about 0.005 M
to about 0.5 M, more specifically about 0.01 M to about 0.1 M.
The graphene may be contacted with the solution comprising the
inorganic material at a temperature of about 50 to about
100.degree. C., specifically 60 to about 90.degree. C., more
specifically about 70 to about 80.degree. C. for about 10 minutes
to about 4 hours, specifically about 20 minutes to about 2 hours,
more specifically about 40 minutes to about 1 hour.
According to another embodiment, the graphene may be formed on a
substrate to form a graphene coated substrate. The substrate may be
any of the various substrates disclosed above. The inorganic
material may then be disposed on the graphene coated substrate.
One or more embodiments will be disclosed in further detail with
reference to the following examples. These examples are for
illustrative purposes only and are not intended to limit the scope
of the disclosed embodiments.
Example 1
Zinc acetate powder having the formula
(C.sub.2H.sub.3O.sub.2).sub.2Zn was dissolved in ethanol to prepare
a 0.01 M solution. Then, the prepared 0.01 M solution was
spin-coated or dip-coated on a graphene coated polyethylene
terephthalate ("PET") plastic substrate having the dimensions 2
cm.times.2 cm, thereby forming a ZnO seed layer. The plastic
substrate coated with graphene, on which the ZnO seed layer was
formed, was immersed in a solution for growing ZnO in order to grow
a ZnO nanorod. The ZnO growth solution was prepared by dissolving
zinc nitrate having the formula Zn(NO.sub.3).sub.2.6H.sub.2O and
hexamethylenetetramine ("HMT") having the formula
C.sub.6H.sub.12N.sub.4 in 250 milliliters (ml) of deionized ("DI")
water. The prepared ZnO growth solution had a concentration of
0.025 M Zn nitrate, 0.025 M HMT and DI Water. The plastic
substrate, having the ZnO seed layer, was immersed in each of the
prepared ZnO growth solutions and then the temperature was
increased to 95.degree. C. and held for 3 hours, thereby
synthesizing the ZnO nanorod on the graphene coated plastic
substrate. The formed ZnO nanorod had a length of about 2000 nm and
a diameter of about 100 nm.
FIG. 5 is a scanning electron microscope ("SEM") image of the ZnO
nanorod that has grown vertically with respect to a surface of the
graphene.
FIG. 6A is a transmission electron microscope ("TEM") image of an
interface between the prepared ZnO nanorod and the graphene
according to Example 1. FIG. 6B is an enlarged view of the
indicated portion of FIG. 6A, FIG. 6C is a selected area
diffraction pattern of the upper indicated (i.e., ZnO) portion of
FIG. 6B, and FIG. 6D is a selected area diffraction pattern of the
lower indicated (i.e., graphene) portion of FIG. 6B. Referring to
FIG. 6A, it can be seen that a (0001) plane of the ZnO nanorod is
oriented parallel to a (0001) plane of the graphene at the
interface between the ZnO and the graphene. FIG. 6A shows that a
crystal plane of the graphene and a crystal plane of the ZnO
nanorod are sequentially stacked on a silicon (Si) substrate. FIG.
6B is an enlarged TEM image of the indicated portion of FIG. 6A
showing the stack structure to clarify analysis of the interface
between the graphene and the ZnO nanorod. The top circle 80 in FIG.
6B represents atomic crystal sites of the ZnO nanorod and the
bottom circle 90 represents atomic crystal sites of the graphene.
FIG. 6C and FIG. 6D show an electron diffraction pattern of the
circled portions in FIG. 6B, in which FIG. 6C shows an electron
diffraction pattern of the ZnO nanorod and FIG. 6D shows an
electron diffraction pattern of the graphene. Referring to FIG. 6C,
it can be seen that the atomic crystal sites of the ZnO nanorod are
sequentially and regularly stacked.
Example 2
A ZnO nanorod was grown on a PET substrate coated with indium tin
oxide ("ITO") in the same manner as in Example 1. The ITO layer had
a thickness of about 100 nm. The grown ZnO nanorod had the same
length and diameter as the ZnO nanorod grown on the graphene coated
PET substrate of Example 1. The ITO-coated PET substrate had a
sheet resistance of about 70 ohms per square (ohm/sq), and the
graphene-coated PET substrate had a sheet resistance of about 200
ohm/sq. A nanoscale power generator (i.e., piezoelectric generator)
was manufactured using the substrate in the following manner. A
sample formed by growing a ZnO nanorod on the ITO-coated PET
substrate was used as a bottom plate and the ITO-coated PET
substrate was used as a top plate. The top and bottom plates were
coupled to each other to manufacture the nanoscale power generator,
and an electrode was connected to the ITO of each of the top and
bottom plates, respectively, to measure a current flowing through
the nanoscale power generator. A nanoscale power generator using
graphene may also be manufactured in the same manner as disclosed
above. For example, a sample formed by growing a ZnO nanorod on the
graphene-coated PET substrate was used as a bottom plate and the
graphene-coated PET substrate was used as a top plate. The obtained
top and bottom plates were coupled to each other to manufacture a
nanoscale power generator, and an electrode was connected to the
graphene of each of the top and bottom plates, respectively, to
measure a current flowing through the nanoscale power generator.
FIG. 7A is a graph of current density (microamperes per square
centimeter, .mu.A/cm.sup.2) versus time (seconds, sec) and shows
results of analysis of the nanoscale power generator manufactured
using the ITO-coated substrate. FIG. 7B is a graph of current
density (microamperes per square centimeter, .mu.A/cm.sup.2) versus
time (seconds, sec) and shows results of analysis of the nanoscale
power generator manufactured using the graphene-coated substrate.
When a force of 0.9 kilogram-force (kgf) was applied to each of the
nanoscale power generators, the nanoscale power generator
manufactured using the ITO-coated substrate generated a current of
about 1 .mu.A/cm.sup.2, and the nanoscale power generator
manufactured using the graphene-coated substrate generated a
current of about 2 .mu.A/cm.sup.2. Thus, in an embodiment wherein
graphene, which has a sheet resistance of 200 ohm/sq was used, the
generated power was twice that when ITO, which has a sheet
resistance of 70 ohm/sq, was used, despite the fact that the sheet
resistance of the graphene was three times greater than that of the
ITO. These results show that the parallel stacking of a (0001)
plane of graphene and a (0001) plane of the ZnO nanorod provides a
decrease in interfacial defects and more efficient movement of
electric charge.
In addition, after the above described compressing of the nanoscale
power generator manufactured using the graphene-coated substrate,
the electrodes were reversed and the nanoscale power generator
having the graphene-coated substrate was compressed an additional 5
times with a force of 0.9 kgf. The results of these additional
compressions, which is also shown in FIG. 7B, show that the
nanoscale power generator having a graphene-coated substrate
generated a current of about -2 .mu.A/cm.sup.2. Because nanoscale
power generator generated a current of about the same magnitude in
both the forward and reverse directions, the nanoscale power
generator has a forward field direction which is about the same as
a reverse field direction.
As described above, according to the one or more of the above
embodiments, in the material comprising graphene and an inorganic
material, defects at the interface between the graphene and the
inorganic material are minimized and thus an interfacial resistance
is reduced and thus, electrical charge flows more efficiently. In
addition, because the cost of graphene is relatively low, the
material may be used in various electrical devices, such as a light
emitting diode ("LED"), a solar cell, or a power generator, for
example.
It should be understood that the exemplary embodiments described
therein should be considered in a descriptive sense only and not
for purposes of limitation. Descriptions of features or aspects
within each embodiment should be considered as available for other
similar features or aspects in other embodiments.
* * * * *